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Arc Flash DefinitionsDEFINITIONS
Approach Boundaries (Shock Protection Boundaries): Satisfactory distances between a qualified and unqualified person and conductors that have not been placed in an electrically safe work condition. There are three types of Approach Boundaries: Limited, Restricted and Prohibited. Limited Approach Boundary: An approach limit at a distance from an exposed live part within which a shock hazard exists. Restricted Approach Boundary: An approach limit at a distance from an exposed live part where there is an increased risk of shock, due to electrical arc over combined with inadvertent movement, for personnel working in close proximity to live parts. Prohibited Approach Boundary: An approach limit at a distance from an exposed live part within which work is considered the same as making contact with that the live part.
Arc Flash: The passage of current through air between phase conductors or phase conductors and neutral and ground. This is initiated by a flashover, or from the introduction of some conductive material.
Arc Flash Hazard: A dangerous condition associated with the possible release of an electric arc
Arc Flash Hazard Analysis: A study investigating a worker’s potential exposure to arc flash energy, conducted for the purpose of injury prevention, the determination of safe work practices, and the appropriate levels of PPE.
Arc Flash Protection Boundary: When an arc flash hazard exists, an approach limit at a distance from a prospective arc source within which a person could receive a second degree burn if an electrical flash were to occur.
Arc Flash Suit: A complete FR clothing and equipment system that covers the entire body, except for the hands and feet. This includes pants, jacket, and beekeeper-type hood fitted with a face shield.
Arc Rating: The value attributed to materials that describers their performance to exposure to an electrical arc. It is expressed in cal/cm2 (calories per centimeter squared).
ATPV: Arc Thermal Performance Value: This value is presented in cal/cm2 and represents the maximum capability for arc flash protection of a specific garment.
Balaclava: An arc rated sock hood that protects the neck and head except around the eyes and nose.
Cal/cm2: Calories per centimeter squared: The amount of energy that can result from an electric arc flash is measured is measured in cal/cm2. Once this is known, the ATPV rating is also known.
Calorie: The energy required to raise one gram of water one degree Celsius at one atmosphere. The onset of second-degree burns may occur at 1.2 calories per centimeter squared per second. This is equal to holding your finger over the tip of the flame of a lighter for one second.
De-energized: Free from any electrical connection to a source of potential difference and from electrical charge; not having a potential different from that of the earth.
Electrical Hazard: A dangerous condition such that contact or equipment failure can result in electric shock, arc flash burns, thermal burns, or blast.
Electrically Safe Work Condition: A state in which the conductor or circuit part to be worked on or near has been disconnected, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.
Electrical Shock: A condition caused by the release of energy by contact with an exposed conductor or part. Electric shock from common 60Hz AC power passing from hand to foot for a period of 1 second can have the following results: Current Effects 1-3 Milliamps Tingling Sensation 3+ Milliamps Shock, Pain 10+ Milliamps Muscular Contractions (unable to let go) 30+ Milliamps Respiratory Paralysis (may be fatal) 60+ Milliamps Extreme Pain, Respiratory Arrest, Severe Muscle Contractions, Ventricular Fibrillation (usually fatal) 4+ Amps Heart Paralysis, Nerve Damage (fatal) 5+ Amps Cardiac Arrest, Tissue & Organ Burning (fatal)
EBT (Energy Breakopen Threashold): Basically, the physical strength of a fabric with respect to thermal energy and at what arc flash value the fabric will fail. Breakopen is when one or more holes are formed in the innermost layer of material that would allow flame to pass through the material.
FR Flame-Resistant: The property of a material whereby combustion is prevented, terminated, or inhibited following the application of a flaming or non-flaming source of ignition, with or without subsequent removal of he ignition source.
Hazard Risk Category (HRC): Categories defined by NFPA 70E® defining levels of protection required when performing tasks. Current HRC levels are 1, 2, 3 or 4, which require the following minimum levels of protection: HRC1 4cal/cm2, HRC2 8cal/cm2, HRC3 25cal/cm2, HRC4 40cal/cm2 *When incident energy exceeds 40cal/cm2 at the working distance, greater emphasis than normal should be placed on de-energizing before working on or near exposed electrical conductors or circuit parts
Incident Energy: The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. One of the units used to measure incident energy is calories per centimeter squared (cal/cm2).
Qualified Person: One who has the skills and knowledge related to the construction and operation of the electrical equipment and installations and has received sufficient training to recognize and avoid the hazards involved.
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